The invention concerns a method for the production of a container having a casing constituting the container body made from composite carton whose inner side is covered by a barrier layer and a plastic layer deposited thereon, in which one end of the casing is rolled-over in an outward direction to form a curled edge and a membrane is subsequently sealed to the upper crown of the curled edge. A bottom is attached at its opposite end after the container is filled.
Composite carton containers of the above mentioned kind are often used for the packaging of pourable, in particular powder-like or granular materials or also for fluid products having a viscous or pasty consistency. In order to protect the quality of the fill product the composite carton container must be sealed, wherein, in dependence on the fill product, liquid tight or even gas-tight sealing is required. The casings are generally produced through winding of an endless length of material or from a material blank cut to the appropriate length for the casing. In the former case, the casing is cut to the desired size from the produced wound tube by means of a cutting process. Sealing of the casing is guaranteed by a barrier layer e. g. a metal, in particular, an aluminum foil layer, laminated onto the normally multi-layered base of recycling carton material and then covered by a thin plastic layer. Overlapping edges of the length of material or of the material blank are sealed along the winding seam.
The casing is rolled over in an outward direction at the end subsequently forming the removal opening to form a curled edge for maintaining the open cut edge of the casing and for protecting it against the entrance of liquids as well as to facilitate sealing of a membrane onto the outer plastic coating of the curled edge, the sealing membrane having a corresponding plastic coating on its inside. In this manner, a gas and liquid tight first-opening seal is also fashioned in the region of the removal opening. However, in practice, leaks often occur near the sealed membrane, whereas the bottom, which is introduced onto the opposite end subsequent to filling, is easily rendered leak proof.
With sheet metal containers having fundamentally similar construction (EP 0806 370), the sheet metal blank is dipped into liquid plastic after rolling the curled edge. This plastic then hardens to an enlargement on the curled edge having a thickness which is difficult to control. The membrane is sealed onto this relatively thick plastic layer. This procedure requires a separate dipping step which is an additional production step and is also time consuming, since one must wait until the plastic layer has polymerized. When the sealing membrane is removed, residual plastic irregularities remain on the edge and loosened plastic particles can fall into the filled product which is not tolerable for food products.
With composite carton containers, the unexpected leakage in the vicinity of the sealed membrane is probably due to the fact that, when rolling over the curled edge in an outward direction, the plastic laminate is thinned or even torn due to material stretching. Cracks in the barrier layer can also occur.
It is therefore the underlying purpose of the invention to further improve the above mentioned method for the production of composite carton container in such a manner that the gas and liquid sealing in the vicinity of the sealed membrane is as good as the sealing over the entire remaining regions of the casing.